Acoustic linings

ABSTRACT

The invention provides an acoustic lining, suitable for a gas turbine engine, the lining comprising an impervious sheet, a channel layer, a first porous sheet, a honeycomb layer and a second porous sheet, the channel layer being secured to the impervious sheet and the first porous sheet and the honeycomb layer being secured between the first and second porous sheets.

D United States Patent [1 1 3,640,357 Kitching et al. 1 Feb. 8, 1972[54] ACOUSTIC LININGS 3,113,634 12/1963 Watters ..18l/33 G [72]Inventors: Anthony George Kmhing Derby; Me 3,166,149 1/1965 Hulse et al....181/33 R Brown Ticknan both England 3 3,502,171 3/1970 Cowan...181/33 R 3,507,355 4/1970 Lawson ..l81/33 G [73] Assignee: RollsRoyce Limited, Derby, England Primary ExaminerRobert S. Ward Jr. 1 a 1[22] Flled Feb 19 Attomey-Cushman, Darby & Cushman 21 Appl. No.: 119,308

[57] ABSTRACT [52] U.S.Cl ..l8l/33 G, 181/33 H The invention provides anacoustic lining Suitable for a gas [51] Int.Cl. ..B64d 33/06, E04b l/84,FOln 1/ 10 turbine engine, the lining comprising an impervious sheet, a[58] Field ofSearch ..l81/33 R, 33 G, 33 GA, 32 HA, channel layer, afirst porous Sheet, a honeycomb layer and a 181/33 33 33 50 secondporous sheet, the channel layer being secured to the impervious sheetand the first porous sheet and the [56] Rate" I cued honeycomb layerbeing secured between the first and second UNITED STATES PATENTS P2,870,857 l/1959 Goldstein ..18l/33 G 7 Claims, 2 Drawing FiguresACOUSTIC LININGS This invention relates to acoustic linings forattenuating the noise produced by engines such as gas turbine engines.The linings may for example be used to line the bypass duct of a fanengine or the turbine exhaust and intake of such an engine.

The present invention provides an acoustic lining comprising animpervious sheet, a channel layer, a first porous sheet, a honeycomblayer and a second porous sheet, the channel layer being secured to theimpervious sheet and the first porous sheet and the honeycomb layerbeing secured between the first and second porous sheets. The secondporous sheet may comprise a single discretely perforated metal sheet ora combination of such a metal sheet and a porous fibrous layer.

The maximum width of each channel in the channel layer may beapproximately equal to the width across each cell of the honeycomb layerand the channels may be interconnected by means of slots in the walls ofadjacent channels or by forming some of the walls so that they areporous.

The impervious sheet, the first and second porous sheets and thehoneycomb layer may be metallic and the channel layer may be made fromglass reinforced sheet.

The perforations in the first porous sheet may be larger than theperforations in the second porous sheet and the outer surface of thesecond porous sheet may be provided with an erosion resistant coating.

The layers and the sheets may be secured together by resin bonding andthe honeycomb layer may be secured to the first and second porous sheetsby the method described in our copending British application No.30259/69.

The lining may be formed into a shape suitable for mounting in a gasturbine engine for example it may be annular in cross section formounting in the bypass duct of a front fan engine or for surrounding thecompressor of such an engine.

The present invention will now be more particularly described withreference to the accompanying drawing in which FIG. 1 shows a gasturbine engine incorporating one form of acoustic lining according tothe present invention and FIG. 2 is an enlarged view of a section of theacoustic lining shown in FIG. 1.

Referring to the Figures, 21 gas turbine engine is of the front fan typehaving a fan 12 and compressor means 14 and the fan is mounted forrotation in a duct 16 which is defined by a casing 18. An acousticlining 20 is mounted in the duct 16 and a further lining 22 surroundsthe compressor means 14.

Referring more particularly to FIG. 2, the lining 20 comprises animpervious metallic layer 24, a channel layer 26 and a porous metallayer 28, a honeycomb layer 30 and a second porous metal sheet 32. Thechannel layer 26 is secured to the sheet 24 and the porous sheet 28 byresin bonding and the honeycomb layer 30 is secured to the first andsecond porous sheets 28 and 32 by the method described in our copendingBritish application No. 30259/69.

The layer 26 is fonned from a glass reinforced plastics sheet which isformed into a corrugated shape to provide a plurality of channels 34 andthe maximum width across each channel is approximately equal to thewidth across each cell 36 of the honeycomb layer 30.

The second porous sheet 32 forms the innennost part of the duct 16 andthe channels 34 are arranged to run circumferentially around the duct. I

The walls defining the channels 34 can be slotted or made porous both toimprove noise attenuation and for ease of manufacture, i.e., since thechannels run circumferentially around the duct 16, the channel layer 24can be made by forming the layer in a flat corrugated shape cuttingslits at fairly closely spaced intervals and then bending the flatcorrugated shape into an annulus.

This form of construction allows any moisture which may collect ineither the channel layer 24 or the honeycomb layer 30 to be easilydrained.

- In an alternative arrangement (not shown), the sheet 32 can comprisean outer metal sheet formed with discrete perforations bonded to aninner porous fibrous layer, the combination then bein'glbonded to thehoneycomb layer 30.

While e impervious sheet 24, the perforate sheets 28 and 32 and thehoneycomb 30 have been described as being made of metal they can forexample be made of glass fiber reinforced sheets if the environment inwhich the lining has to operate allows.

The invention has been described in relation to the bypass duct liningand a compressor casing of a jet engine it can equally well be appliedto any other part of a gas turbine engine where noise attenuation isrequired and its use is not restricted to gas turbine engines, e.g., anyduct in which a gas is flowing or for enclosing a space in which noiseis generated.

We claim:

1. An acoustic lining comprising an impervious sheet, a channel layer, afirst porous sheet, a honeycomb layer and a second porous sheet, thechannel layer being secured to the impervious layer and the first poroussheet and the honeycomb layer being secured between the first and secondporous sheets.

2. An acoustic lining as claimed in claim 1 in which the first poroussheet has perforations which are larger in size than correspondingperforations in the second porous sheet.

3. An acoustic lining as claimed in claim 2 in which the maximum widthof each channel is approximately equal to the width across each cell ofthe honeycomb layer.

4. An acoustic lining as claimed in claim 1 in which the channels of thechannel layer are interconnected.

5. An acoustic lining as claimed in claim 4 in which the channels areinterconnected by means of slots formed in the walls of adjacentchannels.

6. An acoustic lining as claimed in claim 4 in which the channels areinterconnected by forming the walls of the channels so that they areporous.

7. An acoustic lining as claimed in claim 1 in which the first andsecond porous sheets are metallic and the channel layer is formed from aglass fiber reinforced composite sheet.

1. An acoustic lining comprising an impervious sheet, a channel layer, a first porous sheet, a honeycomb layer and a second porous sheet, the channel layer being secured to the impervious layer and the first porous sheet and the honeycomb layer being secured between the first and second porous sheets.
 2. An acoustic lining as claimed in claim 1 in which the first porous sheet has perforations which are larger in size than corresponding perforations in the second porous sheet.
 3. An acoustic lining as claimed in claim 2 in which the maximum width of each channel is approximately equal to the width across each cell of the honeycomb layer.
 4. An acoustic lining as claimed in claim 1 in which the channels of the channel layer are interconnected.
 5. An acoustic lining as claimed in claim 4 in which the channels are interconnected by means of slots formed in the walls of adjacent channels.
 6. An acoustic lining as claimed in claim 4 in which the channels are interconnected by forming the walls of the channels so that they are porous.
 7. An acoustic lining as claimed in claim 1 in which the first and second porous sheets are metallic and the channel layer is formed from a glass fiber reinforced composite sheet. 